1. Technical Field
The present invention relates to an image forming device, and in particular, to an image forming device that suppresses banding due to landing interference.
2. Related Art
In an inkjet image forming device, when droplets land on places on the surface of a recording medium such as a sheet or the like at which places droplets that have landed remain, the droplets (dots) that landed previously and the droplets that land thereafter interfere with one another, and the droplets move. This is because the surface energy of two droplets that have landed is small, or is due to the overflowing effect caused by the amount of ink per unit surface area being large. There is the problem that the offset of droplets from their ideal landing positions causes offset in the density distribution that is visually perceived as banding.
In order to overcome this problem, sheets that are specially used for inkjet printing that have a water-absorbing layer are used. In this case, interference between droplets is suppressed because the droplets are quickly absorbed by the sheet specially used for inkjet printing. However, on the other hand, there is the problem that the cost of these sheets that are specially used for inkjet printing is high. Further, there are cases in which image formation is carried out in multiple passes in order to ensure the time for absorption and drying of the dots. However, in this case, the productivity becomes problematic.
Further, in order to improve the productivity, in recent years there have been proposed inkjet printers in accordance with a single-pass method that carry out image formation by the scanning of a single time. In printers using this method, the differences in the landing times of the respective dots are short. Accordingly, banding that is caused by interference between droplets is even more severe.
In relation to the above-described techniques, Japanese Patent Application Laid-Open (JP-A) No. 5-104726 discloses a technique of making the dot mass small in order for the respective dots to not contact one another. JP-A No. 11-151821 discloses a technique of making the brightness of small dots of a high concentration of ink and large dots of a low concentration of ink be the same at intermediate tones. Further, JP-A No. 2006-123522 discloses a technique of changing the landing order in accordance with the overlapping with adjacent dots, and setting the landing time difference to exceed the fixing time.
JP-A No. 2009-154499 discloses a technique of disposing large dots, that cause beading, in the form of a mesh or the form of a line at a fixed pitch so as to avoid beading.
However, in the technique disclosed in JP-A No. 5-104726, when the dots are small, the interval between respective dots widens. Accordingly, it is easy for stripes to become conspicuous (because overlapping is eliminated). When the resolution is increased in order to avoid this drawback, the productivity decreases in the case of multiscanning.
Using different inks as in the technique disclosed in JP-A No. 11-151821 is related to an increase in costs and increased complexity of the device. Further, changing the landing order as in the technique disclosed in JP-A No. 2006-123522 is linked to increased complexity of the device. Moreover, setting the landing time difference to exceed the fixing time leads to a decrease in the productivity.
In addition, if the dots are disposed cyclically as in the technique of JP-A No. 2009-154499, the dots are affected by poor ejection, and it is easy for banding to arise.
In this way, conventional techniques have the problem that banding due to landing interference cannot be suppressed.